The present invention relates, in general, to a method of presenting a video image for display on a consumer television receiver. More particularly, this invention provides a method for improving the appearance of a video image by masking undesirable video artifacts present along the edges of the image using a superimposed framing image.
A digital television set top box is typically capable of various display modes and optional monitor settings. Two common modes that do not employ the entire area of the available image display are letterbox and vertical letterbox. Existing analog television receivers may also display content in letterbox mode. Indeed, this mode is commonly used for content played back from digital video disks (DVDs). In other modes, sometimes referred to as full modes, the outer edges of the displayed video are hidden behind a physical bezel of the display monitor. The hiding of the edges of the image behind the bezel is commonly referred to as overscanning the image. The portion of the image that is hidden behind the bezel is known as the overscan portion.
Overscanning is typically done to hide artifacts which may appear at the horizontal and/or vertical edges of the image. One type of artifact is data, such as closed caption information or electronic program guide information that is digitally transmitted in the vertical blanking intervals of standard analog television signal. When an analog TV image such as may be produced by an television signal corresponding to the National Television Standards Committee (NTSC) format is displayed in letterbox mode, the digital data transmitted in the vertical blanking interval for example, closed caption data on line 20, may appear as one or more lines of rapidly moving white dots above the image. This type of distortion would also be produced for television signals that include teletext or videotex information.
Distortion on the vertical edges of an image may occur, for example, when a video image derived from an analog video cassette recorder (VCR) is displayed. This type of distortion occurs because the horizontal synchronization signal provided by the VCR is not an exact sub-multiple of twice the color subcarrier frequency. In the NTSC standard, for example the color subcarrier frequency is 455/2 times the line scanning frequency. When this constraint is not met, as with signals from analog VCRs, the vertical edges of the image may appear to be wavy. This type of distortion may also occur in images from other nonstandard signal sources, such as video games.
Because the letterbox and vertical letterbox modes do not employ the entire area of the available image display, the outermost edges of the video images are visible to the user. Thus, it is possible that some undesirable video data patterns may be visible to the user.
Additionally, with the emergence of digital set top boxes, it is not possible to predict all the cases of unpleasant video artifacts near the edges of the image due to the various analog to digital conversion techniques employed.
Accordingly, an audio visual device is desired which is capable of adjustably concealing the outermost edges of an available image display for use in operation with such modes as letterbox and vertical letterbox.
The subject invention is embodied in a method of generating an adjustable video display window from an using an on screen display (OSD) bitmap stored in a memory. The adjustable video display window masks undesirable video artifacts from the active portion of the video display. The method includes generating an image pattern which frames the displayed video image to hide artifacts along the edges of the image. This image pattern is produced by a video display processor of either the video display device or the television receiver. Parameters of the video display processor are adjusted to vary the dimension of the generated image pattern to redefine the periphery of an active region of the video display. The OSD image pattern is then mixed with an image signal to construct the OSD image pattern, masking the undesirable video artifacts so that they are to visible to the viewer.
It is to be understood that both the foregoing general description of the invention and the following detailed description are exemplary, but are not restrictive, of the invention.